A lack of Pisaster may lead to … disaster
EDS 240 - HW4
Purple Sea Stars and Pacific Purple Sea Urchins
Introduction
Sea stars and sea urchins play an important role in ocean ecosystems. Sea stars are generally population controllers. Purple sea stars (Pisaster ochraceus) in particular control sea snail, mussel, and urchin populations which allows other species, such as barnacles and algae, to thrive with adequate resources. Additionally, algae provide habitat and food for a plethora of other species - species such as the pacific purple sea urchin (Strongylocentrotus purpuratus), who are herbivores that graze on algae. In addition to algae, urchins will passively wait for detritus (kelp fragments) to float their way. However, in times of scarcity, urchins will hunt kelp forests to feed on.
Kelp forests are essential for ocean health. They provide food, shelter, and other protections for marine life. Additionally, they are an important resource in economic and commercial opportunities explored by humans. As such, maintaining kelp forest health is pertinent to protect the ocean.
Without sea stars, urchins may overgraze kelp. Urchins tend to feed on the “holdfast”, or base root like structure of the kelp. When grazing is focused on the holdfast, kelp forests can be quickly and systematically decimated, as without any anchor, the kelp will be swept away from the current. With urchin overgrazing, “urchin barrens” are created, reducing a thriving ecosystem to a excess of urchins and algae that cover the ocean floor.
With that in mind, I explored intertidal observations of the Pacific purple sea urchin and purple sea stars with the goal of diving more into the emperical relationship between these two sea species. I chose these observations to answer the question:
How do Purple Sea Stars and Purple Urchins interact, and what impact do environmental changes and conservation efforts have on their populations?